and maintaining a good, balanced relationship with them

is to our advantage.

Together, they form the gut microbiome,

a rich ecosystem that performs a variety of functions in our bodies.

The bacteria in our guts can break down food the body can't digest,

produce important nutrients,

regulate the immune system,

and protect against harmful germs.

We don't yet have the blueprint

for exactly which good bacteria a robust gut needs,

but we do know that it's important for a healthy microbiome

to have a variety of bacterial species.

Many factors affect our microbiomes,

including our environment,

medications like antibiotics,

and even whether we were delivered by C-section or not.

Diet, too, is emerging as one of the leading influences

on the health of our guts.

And while we can't control all these factors,

we can manipulate the balance of our microbes

by paying attention to what we eat.

Dietary fiber from foods like fruits, vegetables, nuts, legumes, and whole grains

is the best fuel for gut bacteria.

When bacteria digest fiber,

they produce short chain fatty acids that nourish the gut barrier,

improve immune function,

and can help prevent inflammation, which reduces the risk of cancer.

And the more fiber you ingest,

the more fiber-digesting bacteria colonize your gut.

In a recent study, scientists exchanged the regular high-fiber diets

of a group of rural South Africans

with the high-fat, meat-heavy diets of a group of African-Americans.

After just two weeks on the high-fat, low-fiber, Western-style diet,

the rural African group showed increased inflammation of the colon,

as well as a decrease of butyrate.

That's a short chain fatty acid thought to lower risk of colon cancer.

Meanwhile, the group that switched to a high-fiber, low-fat diet

had the opposite result.

So what goes wrong with our gut bacteria when we eat low-fiber processed foods?

Lower fiber means less fuel for the gut bacteria,

essentially starving them until they die off.

This results in less diversity

and hungry bacteria.

In fact, some can even start to feed on the mucus lining.

We also know that specific foods can affect gut bacteria.

In one recent microbiome study,

scientists found that fruits,

vegetables,

tea,

coffee,

red wine,

and dark chocolate

were correlated with increased bacterial diversity.

These foods contain polyphenols,

which are naturally occurring antioxidant compounds.

On the other hand,

foods high in dairy fat,

like whole milk and sugar-sweetened sodas,

were correlated with decreased diversity.

How food is prepared also matters.

Minimally processed, fresh foods generally have more fiber

and provide better fuel.

So lightly steamed,

sautéed,

or raw vegetables

are typically more beneficial than fried dishes.

There are also ways of preparing food that can actually introduce good bacteria,

also known as probiotics, into your gut.

Fermented foods are teeming with helpful probiotic bacteria,

like lactobacillus

and bifidobacteria.

Originally used as a way of preserving foods

before the invention of refrigeration,

fermentation remains a traditional practice all over the world.

Foods like kimchi,

sauerkraut,

tempeh,

and kombucha

provide variety and vitality to our diets.

Yogurt is another fermented food that can introduce helpful bacteria into our guts.

That doesn't necessarily mean that all yogurt is good for us, though.

Brands with too much sugar and not enough bacteria

may not actually help.

These are just general guidelines.

More research is needed before we fully understand

exactly how any of these foods interact with our microbiomes.

We see positive correlations,

but the insides of our guts are difficult places to make direct observations.

For instance, we don't currently know

whether these foods are directly responsible for the changes in diversity,

or if something more complicated is happening.

While we're only beginning to explore the vast wilderness inside our guts,

we already have a glimpse of how crucial our microbiomes are for digestive health.

The great news is we have the power to fire up the bacteria in our bellies.

Fill up on fibers,

fresh and fermented foods,

and you can trust your gut to keep you going strong.